The present invention relates to an anti-icing system for a gas turbine engine, more particularly such a system which utilizes air bled from the engine compressor to de-ice the forward portion of the gas turbine engine.
When in flight, aircraft will encounter varying atmospheric conditions, some of which, depending upon the geographical location, the season and the flight altitude, may cause ice to form on the aircraft and portions of the aircraft engine. Under such icing conditions, the turbojet engine takes in cold and moist air which may form ice on some of the engine components. The amount of ice formed will depend on various meteorological parameters and features of the aircraft engine. Components located in the front portion of the gas turbine engine, in particular the engine shaft dome or nose and the forward lip of the engine intake housing are susceptible to icing and are insufficiently exposed to dynamic centrifugal forces which might otherwise protect them from substantial ice accumulation in prolonged flights.
A conventional solution to either prevent or eliminate the effects of icing on engine components utilizes heated air tapped or bled from the gas turbine engine compressor. The state of the art is typified by U.S. Pat. No. 3,981,466 which discloses an anti-icing system for the intake lip which includes directly aiming the tapped or bled air from the compressor onto the forward edge of the lip. The temperature of the bled or tapped air varies in direct relationship to the engine speed. The air temperature is relatively low under lower power operating conditions and is relatively high under full power operating conditions. Accordingly, this anti-icing system has low efficiency under lower power operating conditions.
In order to prevent ice build-up, or remove ice from the gas turbine engine nose or dome, air bled from the compressor may be directed onto this portion of the engine. However, the air bled from the engine compressor under full power operating conditions is extremely hot and must be cooled before being directed onto this portion of the gas turbine engine to prevent damage to the front bearing and/or the turbofan due to overheating. To overcome this problem, as noted in U.S. Pat. Nos. 4,485,619 and 4,546,604, air circulation is established in a closed system due to the rotation of the engine shaft nose or dome. As in the previous system, the anti-icing capacity of these systems is a direct function of the mode of operation of the gas turbine engine.